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Understanging HIV

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Douglas Davidson

Chapter 1- Understanding HIV • Why study evolution? o The tools and techniques of evolutionary biology offer crucial insights into matters of life and death • Human Immunodeficiency Virus (HIV) causes Acquired Immune Deficiency Syndrome (AIDS) o HIV is an emerging virus, it rapidly evolves drug resistance and it is deadly • Evolutionary biology is the science devoted to understanding two things: o How populations change through time following modifications in their environment o How new species come into being 1.1- The Natural History of the HIV/AIDS Epidemic • List of worst epidemic in human history according to the number of deaths: o Influenza-50 to 100 million deaths-across the globe o Black Death (1347-1352)-took 30%-50% of the European population-about25 million lives o New World small pox-released in 1520 by European conquistadores-decimated Native American populations across two continents • AIDS is among the worst epidemics in human history o Was first recognized in 1981 o So far infected more than 65 million people o 25 million have already died o By year 2020, a total of 90 million lives would have been claimed by AIDS o According to World Health Organization, AIDS is responsible for about 4.9% of all deaths worldwide o Sub-Saharan Africa is mostly affected by this epidemic • HIV establishes a new infection when a bodily fluid holding the virus, usually a blood or semen, carries it from an infected person directly onto a mucous membrane or into the bloodstream of an uninfected person o Can be passed during heterosexual sex, homosexual sex, oral sex, needle sharing, transfusion with contaminated blood products, childbirth, and breastfeeding • An HIV infection can be acquired only from someone else who already has it! What is HIV? • Like all viruses, HIV is an intracellular parasite that cannot reproduce on its own o It invades specific types of cells in the human immune system o It uses enzymatic machinery and energy of these cells to make copies of itself, killing the host cells in the process • Figure 1.5 (Pg. 7) contains the life cycle of HIV in detail. o The life cycle includes an extracellular phase and an intracellular phase o During the extracellular phase, the virus moves from one host cell to another, and can be transmitted from host to host o Extracellular form of a virus is called a virion, or virus particle o During intracellular or parasitic phase, the virus replicates  HIV initiates its replication phase by latching onto two proteins on the surface of a host cell  HIV then binds to two surface proteins on the target cell called CD4 and coreceptor  This binding fuses the virion’s envelope with the host’s cell membrane and spills the contents of the virion into the cell
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